In crop production, there is a steady demand for stable production of high quality plants and reduction of pesticide dependency. To that end, researchers are actively improving, breeding, and developing plants resistant to pests and pathogenic bacteria through useful plant biotechnologies, such as plant cell fusion and recombinant DNA techniques. Transformed plants resistant to herbicides (Patent Document 1), viruses (Patent Document 2), and pests (Patent Document 3) have been already produced using recombinant DNA techniques. Furthermore, several species of transformed plants resistant to plant pathogenic bacteria, such as the following, have been produced: a transformed plant showing resistance to a pathogenic filamentous fungus, produced by introducing a gene encoding an enzyme that inactivates a toxin produced by the pathogenic filamentous fungus (Non-patent Document 1); a transformed plant showing resistance to at least one pathogenic bacterium, produced by introducing a gene encoding an anti-bacterial protein derived from an insect (Patent Document 4); a transformed plant resistant to complex diseases, produced by introducing a gene derived from Brassica rapa L. var. perviridis) (Patent Document 5); a method for producing a plant resistant to multiple diseases using the thionine gene (Patent Document 6); and a method for producing a plant resistant to complex diseases using an acidic thaumatin-like protein gene (Patent Document 7). However, it is generally accepted that disease resistance obtained by introducing a single resistance gene is not sufficiently effective. Furthermore, some of the introduced genes have harmful effects on the growth, fertility and such of transformants, thereby hindering their practical application.
WRKY transcription factors have been reported to be involved in disease resistance of dicotyledons such as Arabidopsis (Non-patent Documents 2 to 7). In every case hitherto reported on Arabidopsis overexpressing the WRKY transcription factor genes, undesirable characters such as dwarfism, morphological abnormality, and leaf necrosis are reported (WRKY6: dwarfism, reduced apical dominance, leaf necrosis; AtWRKY18: growth inhibition, dwarfism, seed reduction; WRKY70: morphological abnormality, dwarfism). Furthermore, the WRKY transcription factors form a superfamily (about 100 members in rice), which is structurally classified into three groups. Some WRKY transcription factors have been suggested to be involved in morphogenesis and secondary metabolism apart from disease resistance, and each WRKY transcription factor is thought to have an individual function (Non-patent Document 8). The OsWRKY genes of rice have been reported to be involved in ABA-responsive gene expression in aleurone layer; however, the function of these genes in the context of disease resistance is not disclosed in this report (Non-patent Document 9). To date, there have been no reports on the improvement of plant disease resistance by an OsWRKY gene of rice.
Prior art references related to the present invention are listed below.    [Patent Document 1] Japanese Patent Application Kokai Publication No. (JP-A) H2-186925 (unexamined, published Japanese patent application)    [Patent Document 2] JP-A H4-330233    [Patent Document 3] JP-A H3-247220    [Patent Document 4] JP-A H7-250685    [Patent Document 5] JP-A 2004-329215    [Patent Document 6] JP-A 2003-88379    [Patent Document 7] JP-A 2003-199448    [Non-patent Document 1] Windhovel, U., Geiges, B., Sandmann, G. and Boger, P. (1994) Expression of Erwinia uredovora Phytoene Desaturase in Synechococcus PCC7942 Leading to Resistance against a Bleaching Herbicide. Plant Physiol. 104, 119-125.    [Non-patent Document 2] Kalde, M., Barth, M., Somssich, I. E. and Lippok, B. (2003) Members of the Arabidopsis WRKY group III transcription factors are part of different plant defense signaling pathways. Mol. Plant. Microbe Interact. 16, 295-305.    [Non-patent Document 3] Li, J., Brader, G. and Palva, E. T. (2004) The WRKY70 transcription factor: a node of convergence for jasmonate-mediated and salicylate-mediated signals in plant defense. Plant Cell 16, 319-331.    [Non-patent Document 4] Robatzek, S., and Somssich, I. E. (2002) Targets of AtWRKY6 regulation during plant senescence and pathogen defense. Genes Dev. 16, 1139-1149.    [Non-patent Document 5] Yu, D., Chen, C. and Chen, Z. (2001) Evidence for an important role of WRKY DNA binding proteins in the regulation of NPR1 gene expression. Plant Cell 13, 1527-1540.    [Non-patent Document 6] Chen, C. and Chen, Z. (2002) Potentiation of developmentally regulated plant defense response by AtWRKY18, a pathogen-induced Arabidopsis transcription factor. Plant Physiol. 129, 706-716.    [Non-patent Document 7] Asai, T., Tena, G., Plotnikova, J., Willmann, M. R., Chiu, W. L., Gomez-Gomez, L., Boller, T., Ausubel, F. M., and Sheen, J. (2002). MAP kinase signaling cascade in Arabidopsis innate immunity. Nature 415, 977-983.    [Non-patent Document 8] Eulgem, T., Rushton, P. J., Robatzek, S., and Somssich, I. E. (2000). The WRKY superfamily of plant transcription factors. Trends in Plant Sci. 5, 199-206.    [Non-patent Document 9] Xie, Z., Zhang, Z. L., Zou, X., Huang, J., Ruas, P., Thompson, D. and Shen, Q. J. (2005) Annotations and Functional Analyses of the Rice WRKY Gene Superfamily Reveal Positive and Negative Regulators of Abscisic Acid Signaling in Aleurone Cells. Plant Physiol. 137, 176-189.